This relates generally to imaging devices, and more particularly, to imaging devices with photodiodes having multiple readout paths of different conversion gain.
Image sensors are commonly used in electronic devices such as cellular telephones, cameras, and computers to capture images. In a typical arrangement, an electronic device is provided with an array of image pixels arranged in pixel rows and pixel columns. Each image pixel contains a photodiode for generating charge in response to incident light. In some types of pixels (i.e., active CMOS pixels) the charge generated by the image pixels is stored at a floating diffusion node coupled to the photodiode. Circuitry is commonly coupled to each pixel column for reading out image signals from the image pixels.
Conventional image pixels have a single readout path which transfers charge generated by the photodiode to the floating diffusion node. In such an arrangement, the conversion gain of the pixel is determined by a fixed charge capacity (i.e., capacitance) of the floating diffusion region. Typically, image pixels having fixed conversion gain may be optimized for performance in either high exposure or low exposure image captures, but not both. An image pixel having an adjustable conversion gain may therefore be desirable.
It is within this context that the embodiments described herein arise.